Once you got purified Pu, the rest is very easy. Only 15kg of U235 , or 10kg Pu239 is needed (critical mass) to build one bomb (Rudolf Peierls showed that once you have the critical mass, it will explode throught chain reaction). This is why US is so eager to fight proliferation. Because, if some scientist or engineer in Iran smuggles out a suitcase of Pu239, he can make a bomb and give/sell to the terrorist

Paradoxically, US seems to be okay with Japan's Pu stockpile, perhaps trusting the rigorous procedure of Japanese management (meanwhile needs the yen to support its global missions). (But the numbers are shocking, Japan has enough material to make as much as 4500 bombs any time!)

However, the Japan threat is widely felt across Asia, mainly due to memory of WWII, and by how some (rather influential) factions in Japan has dealt with the WWII lessons.

But there is a solution, which kills two birds with one stone. Transfer control of Rokkasho-Mura to IAEA (or even the US), and supply the surplus (enriched) Pu to Iran and the rest of the world who need the fuel-rod for the power plants (with some mutually agreed pricing method). In fact, any U/Pu enrichment outside the 5 nuclear powers should be controlled by IAEA or one of the 5 powers.

Iran (and others) will no longer have the excuse to develop its Pu enrichment program

The rest of Asia (including even N Korea) will be more comfortable with Japan's situation, and will be more likely to become friend with a Japan with no military ambition

US might not trust IAEA's capability to manage Rokkasho-mura. But US can take over this itself. US already has 100 tons at home, so adding another 45 or 200 tons make no difference. China will trust the enrichment plant in US' hand much more than in Japan's. After all, it was US who fought shoulder to shoulder with China in WWII, and although no one in Asia really say it, without US it is extremely unlikely that the Japanese Imperial Army would be defeated, then or now.

Addressing the Japan problem will assure stability in East Asia, and give a better reason for China to reduce its military spending. One cliche the Pentagon repeatedly raised is why China needs to modernize its defense, assuming that there aren't many threats around China. My answer: there are three major concerns from China's perspective (1) basic equipment renewal like any other country, (2) Japan, (3)Taiwan, but that is more of a deterrance game rather than a concern, see Lee Kuan Yew in Der Spiegel).

Pillsbury thinks that China views US as its military rival. (update: see excerpt here) He is totally wrong. The only reason China is looking at US is because it represents the highest standard in the world, and China is indeed concerned about the US-Taiwan Treaty. Otherwise, there is absolutely no reason that China and US can be involved in any military conflict in this century, or future centuries. The two country may become rival in 50-100 years, but more likely economically. For China to reduce its military spending, the Japan factor must be addressed. US was not, is not, and will not be an enemy of China. Taiwan issue will resolve itself in due time.

Update: I can list dozens of flaws in Phillsbury's argument, perhaps in a separate post later or in the discussion thread here - courtesy of Chenlin, an excerpt for the article as well. See also Thomas Barnett's comments via Simonworld.

The problem for Iran and other non-nuclear nations who wants to pursue their own nuclear energy program is an economical problem, not a military one, nor a political one - on the surface at least. So it should be solved in the economical context. They need to process the nuclear waste (contains low purity Pu isotopes) and it is expensive to import fuel rod. Therefore, they want to build their own enrichment plants to recycle the waste (or use this an an excuse to develop the technology). With a reprocessing center for the world nuclear plant, which charges at fair price, we could expect to eliminate such needs (or excuses). Japan, meanwhile, already has such (surplus) reprocessing capacity and it should surrender control to more responsible insitutions like the US or IAEA, which in turn will manage the reprocessing job or outsource the job to the Japanese engineers who are already wokring there.